Cross-mating of Romanomermis culicivorax and R. communensis (Nematoda: Mermithidae).

Tile genus R o m a n o m e r m i s presently contains seven recognized species, six of which parasitize mosquitoes (2). These species differ morphologically, are geographically isolated, and exhibi t different biological characteristics from one another (e.g., opt imal host species, development times, and temperatures) (1,3). T h e study conducted by Petersen (3) represents the only published a t tempt at cross-mating R o m a n o m e r m i s spp. He crossed R. n ie lseni (Tsai and Grundman) from Wyoming and R. cul ic ivorax Ross and Smith f rom Louisiana but (lid not observe egg development or oviposit ion in any cross-mated females. During investigations of mermi th id parasites of mosquitoes in Manitoba, we encountered R . c o m m u n e n s i s Galloway and Brust parasitizing larvae of Aedes c o m m u n i s (DeGeer) at Goose Creek (2). Sufficient numbers of R. cornmunens is were available to conduct cross-mating exper iments with R. cul ic ivorax from Louisiana. For exper iment 1, in 1975, R . communens i s juveniles emerged in the laboratory from field-collected larvae. Juveniles of R . cul ic ivorax were obta ined from our laboratory stock culture. Juveniles were sexed and separated and R. cul ic ivorax were held up to 4 days at 25 C while R. c o m m u n e n s i s were held up to 7 days at 20 C to ensure that both species would moul t at the same time. Nematodes were then placed in moist silica sand (280 g/60-ml glass jar) in the following combinations: R. cul ic ivorax 30 × 30 9-, 1~. cornmunens i s 30 ~ × 30 ~, R . comrnunens i s x R . cul ic ivorax 30 6 × 30 9, R . cul ic ivorax × R . c o m m u n e n s i s 30 × 30 9, R . c o m m u n e n s i s 30 Q, and R. cul ic ivorax 30 9.